Mi hermana agarró el volante y condujo hasta la playa sin ponerse nerviosa.

They are in the preterite because the sentence describes completed actions in a sequence:

• she took/grabbed the wheel
• she drove to the beach

That is exactly the kind of thing Spanish often uses the preterite for: finished events that move the story forward.

If you used the imperfect instead, it would sound more like background description or an ongoing situation, not two clear completed actions.

Because conducir is an irregular preterite verb.

Its preterite stem changes from conduc- to conduj-, and then it uses the special irregular preterite endings:

• yo conduje
• tú condujiste
• él/ella condujo
• nosotros condujimos
• vosotros condujisteis
• ellos condujeron

This pattern is similar to verbs like:

• decir → dijo
• traer → trajo
• traducir → tradujo

So condujo has to be learned as part of that irregular pattern.

Here, el volante means the steering wheel.

In other contexts, volante can mean other things too, depending on the country or situation, but in this sentence the meaning is clearly steering wheel because of the verb condujo.

So agarró el volante is a natural way to say she grabbed/took hold of the steering wheel.

Spanish often uses the definite article (el, la, los, las) where English would use a possessive like his, her, my.

So instead of saying her steering wheel, Spanish often just says the steering wheel, especially when it is obvious whose thing it is from the context.

This is very common with:

• body parts
• clothing
• personal belongings
• things closely connected to the situation

So agarró el volante sounds natural, whereas agarró su volante would usually only be used if you really needed to emphasize ownership.

Both can be possible, but they are slightly different in feel.

• a la playa = to the beach
• hasta la playa = as far as / all the way to the beach

Here hasta emphasizes the destination as an endpoint. It suggests she kept driving until she reached the beach.

So condujo hasta la playa gives a stronger sense of the whole trip reaching that final point.

Because after sin when Spanish means without doing something, it normally uses an infinitive:

• sin hablar = without speaking
• sin mirar = without looking
• sin ponerse nerviosa = without getting nervous

Since ponerse nervioso/a is a reflexive verb, the reflexive pronoun se must stay with it. When a reflexive verb is in the infinitive, the pronoun is usually attached to the end:

• ponerse
• levantarse
• irse

So:

• sin ponerse nerviosa = without getting nervous

Because nerviosa is an adjective that agrees with mi hermana, which is feminine singular.

Agreement here works like this:

• mi hermano ... sin ponerse nervioso
• mi hermana ... sin ponerse nerviosa

Even though the adjective comes after an infinitive phrase, it still describes the subject of the sentence.

Because ponerse + adjective often means to become or to get a certain state.

So:

• estar nerviosa = to be nervous
• ponerse nerviosa = to get nervous / to become nervous

In this sentence, the idea is not simply that she was or wasn’t in a nervous state. It is that she managed to do everything without becoming nervous.

That makes ponerse nerviosa the natural choice.

Because Spanish usually doesn’t need subject pronouns when the verb ending already makes the subject clear.

Here:

• agarró
• condujo

both clearly refer to she in this context, and the sentence already starts with Mi hermana, so repeating ella would be unnecessary unless you wanted emphasis or contrast.

Spanish is much more comfortable than English with leaving subject pronouns out.

Yes, it is understood and used, but the exact feel can vary by region and context.

In Spain, for this kind of sentence, you might also hear:

• cogió el volante
• agarró el volante

Both can work. A useful note for learners is that coger is extremely common in Spain, but in many Latin American countries it can have a vulgar meaning, so some learners see agarrar or tomar more often in neutral materials.

So for Spanish from Spain, agarró el volante is fine, though cogió el volante would also be very common.

No. In this expression, ponerse nerviosa is an idiomatic reflexive phrase meaning to get nervous or to become nervous.

So the whole phrase means:

• without getting nervous
• without becoming nervous

It does not mean she actively caused herself to feel nervous. It just describes a change of state that did not happen.

It has a very common Spanish pattern:

subject + verb + object + y + verb + complement + sin + infinitive phrase

Breaking it up:

• Mi hermana = subject
• agarró el volante = first completed action
• y condujo hasta la playa = second completed action
• sin ponerse nerviosa = manner/result: she did it without getting nervous

So the sentence tells a short sequence of actions and then adds how she managed to do them.

You could, but the meaning would shift a little.

• sin ponerse nerviosa = without getting nervous
• sin estar nerviosa = without being nervous
• sin nervios = calmly / without nerves, more compressed and slightly different in tone

The original version is especially good because it focuses on not becoming nervous during the situation, which sounds very natural here.